Study design and participants
The study had a cross-sectional design and included pregnant women who were registered for and received routine prenatal care in an obstetrics and gynecology facility at a specialist tertiary hospital in Shanghai, China between May 2021 and March 2022. Women were eligible to participate in the study if they were aged 18 years or older, able to read and understand questions, and able to provide written informed consent. Women with serious comorbidity (e.g., cardiovascular disease, anemia, or asthma), poor mental health status, or a physical disability were excluded.
Ethical approval
The study protocol was approved by our institutional ethics committee (approval number 202123). All study participants provided written informed consent after receiving a verbal and written explanation about the purpose of the study and its procedures and being informed that they could withdraw from the study at any time for any reason.
Sample size
The sample size was calculated using the formula [23] with a 95% confidence level, a precision level of 3%, and the prevalence of physical inactivity during pregnancy of 42.9% (p=0.429) as follows:
p=0.429, q=1-p=571, e=0.03, z=1.96
Added a further 10% to allow for no-response in a required sample size of at least 1046. Finally, 1636 pregnant women were enrolled in the study.
Measures
Main outcome
The International Physical Activity Questionnaire short form (IPAQ-SF) has been recommended as a cost-effective method for assessment of the PA level in the general population, including pregnant women, and to have moderate to high reliability (rw=0.59) and concurrent validity (rw=0.55) [24]. Different types of activity are assigned different MET values based on a standard reference [25]. One MET is equivalent to the energy expenditure of sitting 1 hour quietly [26]. There are seven items in the IPAQ-SF [25],six of which are related to the frequency and duration of PA including walking (3.3 MET), moderate-intensity physical activities (4.0 MET) like, yoga, Tai Ji, bicycling at a regular pace and playing table tennis, and vigorous-intensity physical activities (8.0 MET) such as swimming, running, rope skipping and aerobics, etc. Total energy expenditure (TEE) was derived by summing MET scores from each activity multiplied by total weekly minutes.
Covariates and other measurements
Sociodemographic, behavioral, obstetric, and social support data were collected using a structured questionnaire that was developed in consultation with experts in the field and pilot tested in 10 respondents before the survey. The sociodemographic characteristics consisted of age, ethnicity, level of education, current employment status, personal monthly income, and pre-pregnancy body mass index (BMI), which was calculated as body weight divided by the square of height. Using the Chinese classification, women with a BMI <18.5 kg/m2 are considered underweight, those with a BMI of 18.5–23.9 kg/m2 as normal weight, those with a BMI of 24–27.9 kg/m2 as overweight, and those with a BMI ≥28 kg/m2 as obese [27]. The behavioral characteristics before pregnancy are briefly described below. Regular exercise before pregnancy was defined as having consciously engaged in walking, cycling, yoga, running, or other PA for at least 30 min/week in the preconception period [28]. Pre-pregnancy smoking was defined as daily or intermittent smoking and passive smoking was defined as breathing second-hand tobacco smoke for more than 15 minutes a day in the 3 months before conception. Alcohol consumption before pregnancy was defined as drinking at least half a bottle of beer, 40 mL of white wine, or 125 mL of red wine in a month. The obstetric parameters included history of spontaneous abortion, parity, stage of pregnancy, singleton pregnancy, nausea and vomiting during pregnancy, measures taken to prevent miscarriage, and GDM. Questions about social support, including from family, friends, and health care providers, were also covered in the questionnaire.
Prenatal sleep quality was measured using the Chinese version of the Pittsburgh Sleep Quality Index (PSQI), which is the most frequently used generic measure of sleep in the research and clinical settings and has strong reliability and validity [29]. The PSQI includes 19 self-rated questions, which are divided into seven domains, including subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The score in each domain of the PSQI ranges from 0 to 3 and the total score ranges from 0 to 21. A total PSQI score of >5 indicates poor sleep quality and a total score ≤5 is regarded as good sleep quality [30].
Prenatal anxiety status was assessed using the Chinese version of the Self-rating Anxiety Scale, which contains 20 items and is scored by calculating the frequency of symptoms corresponding to anxiety in the past week. Each item is scored on a 4-point scale ranging from 1 to 4; the scores for the 20 items are then added to obtain a rough score, which is then multiplied by 1.25 and the integer component taken to derive the standard score. The cut-off score for this scale is 50 points; a score of 50–59 is classified as mild anxiety, 60–69 as moderate anxiety, and >70 as severe anxiety[31].
Prenatal symptoms of depression were measured by the Edinburgh Postnatal Depression Scale, which is considered to have acceptable reliability, validity and applicability as a screening tool for depression during pregnancy [32]. This scale contains 10 items, each of which is scored from 0 to 3, with higher scores indicating a higher likelihood of perinatal depression. In general, a cut-off score of 10 or higher is recommended for detection of potential depression in pregnant Asian women [33].
Statistical analysis
The characteristics of the participants are presented as descriptive statistics. Continuous variables are summarized as the mean ± standard deviation if normally distributed and as the median (interquartile range) if not. Categorical variables are shown as the frequency (percentage). The dependent variable in this study was physical inactivity, which was defined as total energy expenditure <600 MET min/week. A binary logistic regression model was used to identify factors associated with physical inactivity in pregnant women and control for potential confounding variables. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. The steps used to identify these factors were as follows. First, we used backward elimination to remove variables with a p-value >0.2. Second, considering maternal age, level of education, pre-pregnancy BMI, parity, and history of spontaneous abortions to be clinically relevant or related to the level of PA in previous studies [19, 20, 23], we also added these five variables into the model. Finally, maternal age, level of education, current employment status, personal monthly income, pre-pregnancy BMI, regular exercise before pregnancy, alcohol consumption before pregnancy, history of spontaneous abortions, parity, stage of pregnancy, nausea and vomiting during pregnancy, and prenatal sleep quality were entered as independent variables into the logistic regression model. All statistical analyses were performed using the SPSS software package (version 25.0; IBM Corp., Armonk, NY, USA). A p-value of <0.05 was considered statistically significant.